NRG researches new nuclear reactor concept

Dutch institute generates data for future molten salt reactor

PETTEN – NRG in Petten has started with an irradiation in August which will yield new data on the safe operation of molten salt reactors. This reactor type has potential for increased passive safety and decreased production of long-living radioactive waste compared to existing nuclear power plants.

Existing power plants use enriched uranium as the fuel and water at high pressure as the coolant. A molten salt reactor is suitable for operation with thorium-based fuel carried by a liquid salt mixture which is also the coolant. The design of a molten salt reactor removes the risk of core melt. Such a ‘meltdown’ takes place in existing power plants after evaporation of the coolant, as occurred in 2011 in Fukushima, Japan. ‘Meltdown’ can be avoided in molten salt reactors because it is operated at low pressure, the fission chain reaction is stopped when the temperature in the reactor increases and the salt is automatically flushed to a safe location if needed. In addition, the earth crust contains much more thorium than uranium and less long-living radioactive waste remains after operation of thorium-based molten salt reactors. For these reasons, world-wide interest in this form of nuclear energy, which can contribute to CO2-free energy production in the longer term, is increasing.  Within the framework of the Dutch government to reduce CO2 emissions with at least 90%, NRG studies the perspective of Molten Salt technology as part of the nuclear research programme funded by the Ministry of Economic Affairs.

NRG started an irradiation of a mixture of lithium and thorium fluoride salts on the 10th of August, which have been placed in the High Flux Reactor (HFR) in Petten inside a dedicated irradiation facility. The experiment is performed to investigate the stability of the salt mixture during and after irradiation, the evolution of (fission) gases and the effect of the salt on surrounding materials. This type of information is important for designers of future molten salt reactors, and can be used to answer questions such as which materials can be used as containment materials for the salt?, and what are the most suitable salt mixtures?

The experiment was originally planned to start last year, but because of a lack of previous experience at NRG with molten salt irradiations, additional research was carried out to ensure safe operation under all circumstances. ,,Safety is of overriding priority at NRG. We have used an extra year to investigate different scenarios in which safety and/or quality of the experiment could be compromised. Now that we know that the design of the irradiation facility is adequate, we can start the experiment’’, says project manager Irene Bobeldijk.    

The molten salt reactor was conceived by the American nuclear scientist Alvin Weinberg. In the 1960s an experimental reactor was operated for five years in the Oak Ridge National Laboratory (US), which has produced a lot of useful knowledge and operating experience. This was long ago however, and according to Bobeldijk more and more detailed knowledge is needed today. “It has been some time since a similar molten salt fuel has been irradiated. Our research can contribute to the renewed interest by providing well-founded data.’’

The research is performed in collaboration with the Joint Research Centre of the European Commission in Karlsruhe, which has synthesized the fuel and will investigate samples in their laboratories after irradiation. All findings will be shared with the international community and will become generally available.